I use a subscribed threads folder called To Be Installed? for this exact purpose, then when I install I move the thread to another folder called Installed Hacks.
It works for me, but then again I think I probably have about 50% of the subscribed threads folders in my profile as I like to file things in easy to access places.
I do the same...this would indeed be a nice thing to have.
I also would love to see that here ... not just on the hack forums either, but also for use on threads in Modification discussion, as there are a lot of 'in progress' stuff that tends to go in there before release........